With a continuing quest for lighting apparatus which is low-cost and energy efficient, LEDs have proven to provide light sources which are inherently energy efficient and with advances in LED technology, continue to increase power efficiency as well as life. Further improvements in overall efficiency are sought by efforts to improve the utilization of light output being directed into a desired lighting area. Being that LEDs used as light sources are typically of a small size, there is an additional cost-efficiency and other benefits because the fixtures can be more compact, thereby, for example, reducing material usage, weight, and wind resistance for LED lighting apparatuses.
Lighting systems for various uses typically require the prevention of stray light entering areas not intended to be lit. For example, roadway and parking lot lighting systems are designed to have high levels of light distribution over areas which are to be lighted, while neighboring regions are as free of light as possible. For example, outdoor lighting should not emit light “upward” into the sky. That is, there is a need to be able to direct light in a desired downward and lateral direction onto a predetermined section of property while avoiding light distribution onto an adjacent property. Commonly used “predetermined sections of property” may be referenced according to IES standards for “large area” lighting patterns on a planar surface such as the “ground”. Well-known IES standards for “Type II, Type III, Type IV, and Type V” illuminance patterns are particularly relevant, wherein Type V is “straight-down” lighting with a square boundary (e.g., for parking lot lighting), and the other Types II-IV specify generally rectangular area boundaries that are laterally offset in a preferred direction. Satisfying such concerns can be difficult when LEDs are used as a light source because typically many LEDs are used in a fixture, so light output from an extended light source is particularly difficult to direct into a reasonably uniform level of illumination confined within the boundaries of a prescribed illuminance pattern.
It would be desirable to have an improved efficiency LED light fixture with directional features that improve the illuminance (lighting level) uniformity within a predetermined “large area” lighting pattern. It is further desirable to maximize the amount of light that is directed into the predetermined lighting pattern while minimizing light falling outside the boundaries of the pattern, most particularly for patterns that are offset in a preferential direction from the LED light fixture.